Rate Constants for Hydrogen Atom Transfer Reactions from Bis(cyclopentadienyl)titanium(III) Chloride-Complexed Water and Methanol to an Alkyl Radical

Abstract

Rate constants for hydrogen atom transfer reactions of the water, deuterium oxide, and methanol complexes of bis(cyclopentadienyl)titanium(III) chloride with the secondary alkyl radical 1-cyclobutyldodecyl (2) were determined using indirect kinetic methods. The rate constant for reaction of Cp₂Ti^IIICl−H₂O in THF at ambient temperature was 1.0 × 10⁵ M⁻¹ s⁻¹, and the kinetic isotope effect was k_H/k_D = 4.4. In benzene containing 0.95 M methanol, the rate constant for reaction of the Cp₂Ti^IIICl−MeOH at ambient temperature was 7.5 × 10⁴ M⁻¹ s⁻¹. An Arrhenius function for reaction of the Cp₂Ti^IIICl−H₂O complex in THF was log k = 9.1 − 5.5/2.3RT (kcal/mol). The entropic term for reaction of Cp₂Ti^IIICl−H₂O was normal, whereas the entropic term previously found for reaction of the Et₃B−H₂O complex with radical 2 was unusually small (Jin, J.; Newcomb, M. J. Org. Chem.2007, 72, 5098).